Support echoing output from other clients

in the zmq console

Can result in outputs like:

```
In [1]: 1
[remote]In [1]: 1
[remote]Out[1]: 1
[remote]In [2]: 3
[remote]Out[2]: 3
Out[3]: 1
```

Note that there will be inconsistencies in prompt numbers
because some execution may take place after the in-prompt is drawn.
add ConsoleWidget.include_other_output

matches zmq console. Doesn't include `[remote] ` prefix,
because true async output makes it less important.
highlight input from other front ends

in qtconsole
Merge pull request #6123 from minrk/zmq-console-echo-other

Support echoing output from other clients